The procedural approach according to the invention with the characteristics of the independent procedural claim has in contrast the advantage that the diagnosis can be implemented without an intervention into the normal operation of the internal combustion engine and without an intervention into a metering of a reducing agent into the exhaust gas region of the internal combustion engine, which if need be is present. In this way, a deterioration of the exhaust gas values resulting from the latter aforementioned intervention is avoided. Up until now said deterioration has been taken for granted. A suitable general set-up is being sought for the implementation of the diagnosis.
Advantageous modifications and embodiments of the procedural approach according to the invention result from the dependent claims.
Provision is made in one embodiment for the change in at least the one parameter of the exhaust gas to be detected using at least one calculated parameter of the exhaust gas. An additional exhaust gas sensor can be omitted with this step.
Provision is made in one embodiment for at least a measurement for the load of the internal combustion engine and/or for the rotational speed of the internal combustion engine and/or a measurement for the exhaust gas recirculation rate to be used as an operating parameter of the internal combustion engine. The aforementioned parameters are known by a control unit so that additional sensors are not required.
During the evaluation of the sensor signal supplied by the exhaust gas sensor, respectively of at least one measurement for the sensor signal, provision is advantageously made for the diagnosis to only then be implemented if at least the one operating parameter of the internal combustion engine and/or at least the one parameter of the exhaust gas initially lie below a first threshold value for a specified first time period and subsequently lie above a specified ramp. In this way it can be assured that a definite change in at least the one exhaust gas parameter, which can be detected by the exhaust gas sensor, exists upstream before the exhaust gas sensor.
Provision is made in a modification of this embodiment for the diagnosis to only then be implemented if at least the one operating parameter of the internal combustion engine and/or at least the one parameter of the exhaust gas subsequently lie above a second threshold value for a specified second time period. It can thereby be assured that a sufficiently long change existed.
Provision is preferably made for the diagnosis according to the invention to be carried out at a NOx sensor, which supplies a measurement for the NOx concentration as a sensor signal.
Provision is preferably made in the diagnosis for a test to determine whether the sensor signal, respectively at least a measurement for the sensor signal, increases.
Provision is made in one embodiment for the specification of a delay time, which takes into account the exhaust gas running time and the response time of the exhaust gas sensor.
Provision is made in the diagnosis for a test to determine whether the sensor signal lies above a specified ramp.
A test can be additionally made to determine whether the sensor signal lies above the sensor signal threshold value after exceeding a sensor signal threshold value or at least from a certain point in time up to the end of the second time period.
Provision is made in a more far-reaching diagnosis for a test to determine whether the sensor signal leaves a specified tolerance range at least from the beginning of the second specified time period onwards.
A reliable diagnosis is achieved with these individual steps or preferably with a combination of at least two of the steps.
The device according to the invention for the implementation of the method concerns a control unit, which is specially designed to implement the method.
The control unit preferably contains at least one electric memory, in which the procedural steps are deposited as the control unit program.
Provision is made in the control unit program for all of the steps of the method according to the invention to be executed if the program runs in a control unit.
The control unit program product according to the invention with a program code stored on a machine-readable carrier executes the method according to the invention if the program is executed in a control unit.